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The composition of the tread is an important factor in tire friction. In this paper, which surveys the state of the art, reported effects of composition variables on wet friction of tires are surveyed. Natural rubber and various synthetic rubbers of differing physical properties have been evaluated in a rage of tread compounds differing also in extender oil and carbon black contents. The results show that compounds having high hysteresis also have higher coefficients of friction than low hysteresis compounds. The wet skid resistance of practical tread compounds can be varied by the choice of rubber or rubber blend, amount of extender oil and type of carbon black, listed in order of decreasing effectiveness. Rubbers with higher glass transition temperatures have better skid resistance than rubbers with low transition temperatures. Oil-extended rubbers are better than non-extended rubbers. High structure carbon blacks impart more skid resistance than low structure blacks. It is not practical, however, to pyramid all these effects exclusively for skid resistance since the resultant composition would not meet other criteria of acceptable tire performance including durability and treadwear. Rubbers which are best for skid resistance tend to be poorest for treadwear and vice versa. There are also practical limits for the kind and amounts of extender oil and carbon black that can be used. Modern tread compounds represent judicious choices of composition which satisfy various manufacturing and performance requirements including high skid resistanc and good treadwear. /Author/

This article appeared in Transportation Research Record No. 621, Skidding Accidents: Tires, Vehicles, and Vehicle Components--which contains the proceedings of a conference conducted by the Transportation Research Board, May 2-6, 1977.